The invention relates to aqueous binders.
Air-drying resins or binders are known in particular in the field of alkyd resins; water-dilutable alkyd resins are obtained by mixing (unmodified) alkyd resins with emulsifiers or by incorporating a sufficient number of acid groups which remain following the condensation reaction and neutralizing at least some of them, or by cocondensation with hydrophilic polyoxyalkylene polyols such as polyethylene glycol.
For example, hydroxy-functional emulsifiers for alkyd resins based on polyurethane polyureas are known from EP-A 0 741 156. Other externally emulsified aqueous alkyd resin compositions are described in EP-A 0 593 487. Alkyd resins with a chemically incorporated emulsifier (self-emulsifying) are known from EP-A 0 312 733.
In all cases, compatibility with water is achieved by using nonionic or anionic emulsifiers, in chemically incorporated or added form.
It is also known to modify polyurethane resins, by incorporating unsaturated fatty acids (EP-A 0 444 454), in such a way that coating materials prepared using them are air-drying.
Resins containing epoxide groups, which by modification with fatty acids lead to air-drying binders, are described in EP-A 0 355 761 (esters of fatty acids with epoxy resins), 0 316 732, 0 370 299 (acrylic resins containing epoxide groups) and 0 267 562 (epoxide-ester resins, urethane-alkyd resins or alkyd resins grafted with olefinically unsaturated monomers in an aqueous medium).
Aqueous formulations of neutralized reaction products comprising epoxy resin-amine adducts and fatty acids are known from EP-A 0 070 704. Here, starting from amines and epoxy resins based on polyhydric phenols, adducts with a molar mass of from 1000 to 3000 g/mol are prepared and are subsequently reacted with unsaturated fatty acids to give a product in which the mass fraction of these fatty acids is from 25 to 50%. The amount of the fatty acids in this case is to be chosen such that all of the active amine hydrogen atoms are consumed.
AT-B 390 261 discloses epoxy resin ester emulsions which can be used as binders for air-drying coating materials. The resins are prepared by reacting epoxy resins, partially esterified with fatty acids, and copolymers of unsaturated fatty acids and (meth)acrylic acid, and also further copolymerizable monomers, and to achieve dilutability in water are at least partly neutralized with alkalis. These resins may also be admixed with amino-functional epoxy resin esters.
It has now been found that reaction products of epoxy resins and (optionally fatty-acid-modified) epoxide-amine adducts with an addition of bismuth compounds may be used as binders for air-drying and physically drying coating materials which bring about excellent corrosion protection on metallic substrates.
The invention accordingly provides aqueous binders comprising bismuth compounds D and reaction products Axe2x80x2ABC of epoxy resins Axe2x80x2 containing at least two epoxide groups per molecule and reaction products ABC of epoxy resins A, optionally fatty acids B and amines C, the number-average molar mass Mn of the reaction products Axe2x80x2ABC being at least 5000 g/mol.
xe2x80x9cAqueousxe2x80x9d binders are water-soluble binders and binders which form stable dispersions in water.
In particular, the molar mass calculated from the stoichiometry (number-average), Mn, of these reaction products Axe2x80x2ABC is preferably at least 10,000 g/mol, more preferably at least 15,000 g/mol, and with particular preference at least 20,000 g/mol, and their (measured) acid number is not more than 5 mg/g. Following at least partial neutralization of the amino groups, the reaction products Axe2x80x2ABC can be dispersed in water to give stable dispersions which form no sediment even after the storage at room temperature (20xc2x0 C.) for 4 weeks.
The epoxy resins A and Axe2x80x2 are selected independently of one another from diepoxide or polyepoxide compounds which are obtainable in a known manner by reacting epichlorohydrin with aromatic or (cyclo)aliphatic compounds containing two or more hydroxyl groups per molecule (Taffy process), or may be obtained by reacting diepoxides or polyepoxides with the aforementioned aromatic and (cyclo)aliphatic compounds containing two or more hydroxyl groups per molecule (advancement reaction). Preference is given to epoxy resins based on aromatic dihydroxy compounds, such as bisphenol A, bisphenol F, dihydroxydiphenyl sulfone, hydroquinone, resorcinol, 1,4-bis[2-(4-hydroxyphenyl)-2-propyl]benzene, or aliphatic dihydroxy compounds such as 1,6-hexanediol, 1,4-butanediol, cyclohexanedimethanol, or oligo- and poly-propylene glycol having average degrees of polymerization of between 3 and 40. The specific epoxide group content of the epoxy resins is, independently of one another for the epoxy resins A and Axe2x80x2, in each case preferably from 0.4 to 7 mol/kg, in particular from 0.6 to 6 mol/kg, the epoxide group content of Axe2x80x2 preferably being greater than that of A. In one preferred embodiment, diepoxide compounds are used in each case for A and Axe2x80x2, the specific epoxide group contents being from 0.5 to 4 mol/kg in the case of A and from 2 to 5.9 mol/kg in the case of Axe2x80x2.
Particular preference is given to epoxy resins based on bisphenol A and bisphenol F and mixtures thereof.
The optionally used fatty acids B contain at least one olefinic double bond and have from 6 to 30, preferably from 8 to 26, and in particular from 16 to 22 carbon atoms. Preference is given to palmoleic acid, oleic acid and erucic acid; linoleic acid, linolenic acid and eleostearic acid, arachidonic acid and clupanodonic acid, and also the fatty acids obtainable as mixtures from the naturally occurring oils, such as linseed oil fatty acid, soybean oil fatty acid, conjuvandol fatty acid, tall oil fatty acid, cottonseed oil fatty acid, rapeseed oil fatty acid, and the fatty acid mixtures obtained from dehydrated castor oil.
The amines C are preferably aliphatic, linear, cyclic or branched amines which contain at least one primary or secondary amino group. They have preferably from 2 to 12 carbon atoms and may also contain tertiary amino groups and/or hydroxyl groups as functional groups. Particularly suitable are primary monoamines having from 6 to 12 carbon atoms such as hexylamine, cyclohexylamine, 2-ethylhexylamine and stearylamine, primary diamines such as ethylenediamine, 1,4-diaminobutane and 1,6-diaminohexane, primary-tertiary diamines such as dimethylaminopropylamine, diethylaminopropylamine, diprimary-secondary amines such as diethylenetriamine, 1,9-diamino-5-azanonane, 1,13-diamino-7-azatridecane, triethylenetetramine and tetraethylenepentamine, and the mixtures of oligomeric diaminopolyethyleneimines available commercially as (copyright)Polymin, and also secondary amines and diamines such as piperidine, piperazine, di-n-butylamine, morpholine, and hydroxy-functional amines such as ethanolamine, diethanolamine and diisopropanolamine. It is also possible to use mixtures of said amines.
The intermediates ABC may be prepared by sequential reaction (variant I), in which case the epoxide compounds A are first reacted with the amines C to give a product AC and in a second step these adducts are reacted with the fatty acids B to give the intermediate ABC. A further possibility, however (variant II), is first to react the epoxide compounds A with the fatty acids B to give a product AB and then to react the remaining epoxide groups in AB with the amines C. A further possibility (variant III) is to perform the reaction simultaneously and so in one step to arrive at the intermediates ABC. The amounts of the reactants A, B and C are chosen such that substantially all of the epoxide groups, i.e., at least 90%, preferably at least 95%, and in particular at least 98% of the epoxide groups originally present in A, are reacted. Preferably, the reaction is also to be conducted such that the intermediate ABC no longer contains any reactive amine hydrogen atoms; at the most, however, the amount of amine hydrogen atoms may be 10 mmol/kg.
Where no fatty acids B are used, the reaction of the epoxide A with the amine C is carried out in one stage (corresponding to stage 1 of variant I). It is also possible (as described later on below) to use nondrying fatty acids such as palmitic acid or stearic acid instead of the unsaturated fatty acids B, as a result of which, of course, only physically drying binders are obtained. For the sake of simplicity, however, in the text below even reaction products which contain no fatty acids B or only nondrying (saturated) fatty acids are also referred to as xe2x80x9cABCxe2x80x9d.
A further variant of the present invention comprises, when using amines C containing more than two hydrogen atoms, consuming some of these amine hydrogen atoms by reaction with a monoepoxide Axe2x80x3. Accordingly, a primary amino group containing two active amine hydrogen atoms becomes a secondary xcex2-hydroxyamine group, or a secondary amino group becomes a tertiary xcex2-hydroxyamine group.
Suitable monoepoxides Axe2x80x3 include any desired aliphatic or aromatic monoepoxides or mixtures thereof, especially glycidyl ethers of monohydric alcohols or phenols such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and also glycidyl esters of monobasic acids, preferably aliphatic or aromatic carboxylic acids, such as glycidyl benzoate, glycidyl acetate, glycidyl stearate, and the glycidyl esters of xcex1-branched aliphatic carboxylic acids, such as glycidyl 2-ethylhexanoate, glycidyl 2,2-dimethylpropionate, glycidyl 2,2-dimethyloctanoate, glycidyl 2-methylnonanoate, especially technical-grade mixtures of such branched aliphatic esters, which are available commercially as (copyright)Cardura ES (glycidyl esters of a mixture of xcex1-branched pentanoic acids) or E10 (glycidyl esters of a mixture of xcex1-branched decanoic acids) or (copyright)Glydexx.
In accordance with this variant, the amines C are reduced in their functionality, in whole or in part, prior to the reaction with A or with AB, by the reaction with the monoepoxides Axe2x80x3. These modified amines Cxe2x80x2 are subsequently reacted, alone or in a mixture with the unmodified amines C, with A or with AB (stepwise reaction) or with A and B (conjoint reaction) in the further reaction.
Within the bounds of the invention it is also possible to react the epoxy resins A, before, during or after the reaction with the coreactants B and C, with further compounds E which possess at least one hydrogen atom which is reactive toward epoxide groups and is located in a hydroxyl group or acid group, i.e., alcohols, phenols and acids, especially compounds containing activated hydroxyl groups and acid groups, which are selected preferably from aliphatic diols and polyols such as glycol, propanediol, neopentyl glycol, glycerol, trimethylolpropane, pentaerythritol, ditrimethylolpropane and dipentaerythritol, (substituted) phenols such as phenol itself, the isomeric cresols and xylenols, and also polyhydric and/or polynuclear phenols such as resorcinol, dihydroxybiphenyl, dihydroxydiphenyl sulfone, bisphenol A, xcex1- and xcex2-naphthol, and 2,3- and 2,6-dihydroxynaphthalene, monobasic and polybasic carboxylic acids such as saturated aliphatic linear or branched carboxylic acids having from 2 to 40 carbon atoms, such as isooctanoic acid, stearic acid, the dimeric fatty acids, aromatic carboxylic acids such as benzoic acid, isophthalic and terephthalic acid, sulfonic acids such as benzenesulfonic acid and sulfoisophthalic acid, phosphoric acid, and alkyl- and arylphosphonic acids such as methane- and benzenephosphonic acid.
To prepare the reaction products Axe2x80x2ABC of the invention, the components are reacted preferably in the following amount-of-substance fractions:
per 1 mol of the epoxide compound A, from 0 to 1.0 mol, preferably from 0.1 to 0.9 mol, and with particular preference from 0.25 to 0.8 mol of the fatty acids B, and from 0.5 to 1.9 mol, preferably from 0.6 to 1.75 mol, and with particular preference from 0.65 to 1.5 mol of the amines C are used in the first stage, and then in the second stage from 0.2 to 1.0 mol, preferably from 0.25 to 0.9 mol, with particular preference from 0.3 to 0.8 mol, of the epoxide compound Axe2x80x2 is reacted with the adduct from the first stage.
Where compounds E are used, their mole fraction per 1 mol of the epoxide compound A and/or Axe2x80x2 is from 0.02 to 0.3 mol, preferably from 0.05 to 0.25 mol, and with particular preference from 0.1 to 0.2 mol. The compounds E may be used before the reaction with B and/or C to modify the epoxide compounds; it is also possible to use them together with components B and/or C.
Where monoepoxide compounds Axe2x80x3 are used to modify the amines C, their amount of substance is to be chosen such that the amines Cxe2x80x2 still possess on average at least one reactive amine hydrogen atom per molecule.
Where the epoxide compounds A and/or Axe2x80x2 or the amines C are replaced in whole or in part by these modified compounds in accordance with the two preceding paragraphs, then in each case the mixture or the modified compound is to be used under these conditions for the amount of substance instead of A, Axe2x80x2 and C.
The bismuth compounds D are selected from organic bismuth salts and bismuth chelates. The term bismuth chelates used here refers to bismuth compounds containing organic ligands having at least two atoms per molecule that have free electron pairs, and thus possess at least two adjacent coordination sites of the bismuth central atom with the formation, preferably, of a five- or six-membered ring. Chelating agents for bismuth are, in particular, organic hydroxy acids such as glycolic acid, lactic acid, citric acid, tartaric acid, salicylic acid, dimethylolacetic acid and dimethylolpropionic acid, diphenols such as pyrocatechol and tetrabromopyrocatechol, nitrogen-containing aromatic and aliphatic hydroxy compounds such as 8-hydroxyquinoline, xcex1- and xcex2-amino acids such as alanine, xcex2-alanine, serine and glycine, hydroxy mercaptans such as 2,3-dimercaptopropanol, mercapto acids such as thioglycolic acid, and tertiary amino acids such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid. Organic bismuth salts are derived in particular from strong organic acids such as methanesulfonic acid, trichloroacetic acid, trifluoroacetic acid, and at least dibasic (also chelate-forming) carboxylic acids such as oxalic acid, malonic acid, succinic acid and tricarballylic acid. Preference is given to bismuth salts of amino acids and hydroxy acids, such as bismuth lactate, bismuth glycolate, bismuth bishydroxymethylacetate and bismuth bishydroxymethylpropionate. The bismuth compounds D are used in amounts such that their mass fraction, based on the mass of the solids fraction, is from 0.1 to 20%, the mass fraction of bismuth itself being from 0.01 to 5%, preferably from 0.02 to 4%.
The preparation of the reaction products Axe2x80x2ABC is effected by reaction of components A, B and C preferably in a solvent which is inert under the reaction conditions, at a temperature of from 70 to 150xc2x0 C., the concentration (mass fraction) of components A, B and C (and also, where used, E) in the solution being from 30 to 85%, preferably from 50 to 80%. As solvents it is preferred to use ether alcohols (alkoxyalkanols having from 3 to 10 carbon atoms) such as methoxypropanol, isopropyl glycol, butyl glycol and 3-methoxy-l-butanol. After the end of the reaction (complete consumption of the epoxide groups), the solution of the adduct ABC is neutralized by adding organic or inorganic acids to a degree of neutralization (percentage fraction of those tertiary amino groups which have been converted into the salt form, based on their overall amount) of from 20 to 90%, preferably from 30 to 85%, and in particular from 40 to 80%, and the (partly) neutralized solution of the adduct is diluted with water to a mass fraction of solids of from 20 to 60%, preferably from 25 to 55%, and with particular preference from 30 to 50%. For this procedure the organic solution may be stirred into (preferably preheated) water, or water may be stirred into the organic solution. It is also possible with preference to add part of the acid used for the neutralization, preferably from 20 to 80%, to the water used for dilution. The acids used for neutralization are preferably selected from boric acid, phosphoric acid, formic acid, acetic acid, lactic acid, citric acid and tartaric acid. Subsequently, the bismuth compound D is added to this aqueous solution; the mixture is homogenized thoroughly. The epoxide compound Axe2x80x2 is added slowly to this aqueous solution at a temperature of from 60 to 99xc2x0 C., preferably from 70 to 97xc2x0 C., and with particular preference from 75 to 95xc2x0 C., and the reaction is continued until all of the epoxide groups have been consumed. It is also possible not to add the bismuth compound D until after the reaction of the epoxide Axe2x80x2. Instead of adding the organic or inorganic acids which can be used for neutralization, neutralization may also be brought about simply by adding the (acid-containing) bismuth compound D.
The reaction products Axe2x80x2ABC are suitable for use as binders for preparing aqueous coating compositions which dry physically or in the air by oxidation. The coatings protect the substrate against corrosive attack by acids, alkalis, salt solutions and water. Accordingly, the Bi-catalyzed reaction products of the invention are especially suitable for formulating anticorrosion primers for use on metal sheets or other surfaces of base metals (those below hydrogen in the voltage series), i.e. in particular for sheets of iron, galvanized iron, steel, aluminum, and aluminum alloys. Such coating compositions also include the customary additives such as defoamers, leveling agents, pigments, dispersants, antisettling agents, and thickeners.
Since drying can take place only following application to the substrate (physically or oxidatively), there is no restriction in application in the aqueous binders of the invention by a pot life. In this aspect, they differ advantageously from, for example, two-component (2K) systems which must not be mixed until shortly before application. In comparison to known one-component systems (thermosetting systems) based on epoxy resins, the binders of the invention and the coating materials formulated therefrom feature improved substrate adhesion and improved adhesion of the further paint films applied thereto. Even in thin films above about 15 xcexcm, the corrosion protection properties are already excellent.